1. Evaluation of Cushioning Properties of Running Footwear D. Gordon E. Robertson, Ph.D.* Joe Hamill, Ph.D.** David A. Winter, Ph.D.# * School of Human Kinetics, University of Ottawa, Ottawa, CANADA ** Dept. of Exercise Science, University of Massachusetts, Amherst, USA # Kinesiology Dept., University of Waterloo, Waterloo, CANADA

2. Introduction most mechanical analyses assume rigid body mechanics during initial contact and toe-off the foot may not act as a rigid body especially if footwear is worn modeled as a deformable body, cushioning properties of foot/shoe can be evaluated under ecologically valid conditions

3. Purpose measure the deformation power of foot during running to determine whether the cushioning properties of footwear can be distinguished

4. Methods nine runners (seven male, two female) having men’s size 8 shoe size video taped at 200 fields/second five trials of stance phase of running speed: 16 km/h (4.4 m/s, 6 minute/mile) ground reaction forces sampled at 1000 Hz two conditions: –soft midsole (40-43 Shore A durometer) –hard midsole (70-73 Shore A durometer)

5. Methods foot’s mechanical energy and rate of change of energy computed ( ) E/ ) t) inverse dynamics to calculate ankle force (F) and moment of force (M) ankle force power: P f = F. v ankle moment power: P m = M 

6. Methods power deformation computed as: P def =  E/  t - (P f + P m ) assuming no power loss/gain to/from ground assuming non-rigid (deformable) foot

7. Foot powers 0.000.050.100.150.20 Time (seconds) -2000. -1500. -1000. -500. 0. 500. 1000. 1500. 2000. Power (watts) Trial: F1C1T4 Force power Moment power Total power Energy rate Deformation power

8. Deformation powers 0.000.050.100.150.20 Time (seconds) -2000. -1500. -1000. 500. 0. 500. 1000. Power (watts) Trial: F1C1 soft soles Trial 1 Trial 2 Trial 3 Trial 4 Trial 5

9. Mean deformation powers (subj. J1) Percentage of stance Power (watts) 0102030405060708090100 Hard sole 0102030405060708090100 -2500 -2000 -1500 -1000 -500 0 500 1000 Soft sole

10. Mean deformation powers (subj. F1) 0102030405060708090100 Percentage of stance Power (watts) Hard sole 0102030405060708090100 -2500 -2000 -1500 -1000 -500 0 500 1000 Soft sole

11. Mean deformation powers (subj. L3) Percentage of stance Power (watts) -2500 -2000 -1500 -1000 -500 0 500 1000 0102030405060708090100 Hard sole 0102030405060708090100 Soft sole

12. Mean deformation powers (subj. L4) Percentage of stance Power (watts) -2500 -2000 -1500 -1000 -500 0 500 1000 0102030405060708090100 Hard sole 100

13. Mean deformation powers (subj. L5) Percentage of stance Power (watts) -2500 -2000 -1500 -1000 -500 0 500 1000 0102030405060708090100 Hard sole 0102030405060708090100 Soft sole

14. Mean deformation powers (subj. L6) Percentage of stance Power (watts) -2500 -2000 -1500 -1000 -500 0 500 1000 0102030405060708090100 Hard sole 0102030405060708090100 Soft sole

15. Mean deformation powers (subj. L9) Percentage of stance Power (watts) -2500 -2000 -1500 -1000 -500 0 500 1000 0102030405060708090100 Hard sole 0102030405060708090100 Soft sole

16. Mean deformation powers (subj. L10) Percentage of stance Power (watts) -2500 -2000 -1500 -1000 -500 0 500 1000 0102030405060708090100 Hard sole 0102030405060708090100 Soft sole

17. Mean deformation powers (subj. L11) Percentage of stance Power (watts) -2500 -2000 -1500 -1000 -500 0 500 1000 0102030405060708090100 Hard sole 0102030405060708090100 Soft sole

18. Results in all nine subjects there was an initial period of negative work in six subjects a brief period of positive work followed in seven subjects a period of negative work occurred in midstance in eight subjects there was a period of positive work immediately before toe-off

19. Discussion the initial negative work was assumed to be due to energy absorption by the materials in the heel of the shoe and/or the tissues in the heel the subsequent positive work was likely due to energy return from, most likely, the shoe negative work during midstance may be due to midsole deformation or work by moment at metatarsal-phalangeal joint the final burst of power was assumed to be due to work done by the muscle moment of force across the metatarsal-phalangeal joint

20. Conclusions there was no significant difference between the impact characteristics of the two types of shoe durometer assumption of rigidity of foot-shoe is not appropriate power deformation patterns were consistent within subjects but varied considerably across subjects subjects probably adapted to the shoe impact characteristics to mask the differences in the shoe’s durometer

21. Hypotheses subjects probably adapted to the shoe impact characteristics to mask the differences in the shoe’s durometer need to test methodology on a mechanical analogue that can consistently deliver a footfall to a force platform